Honeywell T874A Thermostat User Manual

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T874A,D Zone Thermostats/  
Q674B,D,E Subbases  
Installation Instructions for the Trained Service Technician.  
See Table 1 for thermostat/subbase and system compatibil-  
Application  
ity; see Table 2 for thermostat specifications. For complete  
Honeywell Trol-A-Temp System specification and appli-  
cation information, refer to the system specification in-  
cluded with the control panel.  
These T874A,D Zone Thermostats and Q674B,D,E  
Subbases provide 24 to 30 Vac temperature control in  
Honeywell Trol-A-Temp heating/cooling zone systems.  
TABLE 1—THERMOSTAT/SUBBASE AND SYSTEM COMPATIBILITY.  
Application  
Thermostat/  
Subbase Model  
Numbera  
Mini-Zone  
Mabs II, Mabs II-L  
Mabs XX  
Stages  
T874A/Q674B Zone 1; conventional  
heat-cool.  
T874A/Q674D Zones other than zone 1; Zones other than zone 1; Not applicable  
Zone 1; conventional  
heat-cool.  
Any zone; conventional heat-cool. Single-stage  
Single-stage  
conventional heat-cool.  
conventional heat-cool.  
T874A/Q674E Not applicable  
Not applicable  
Any zone; conventional heat-cool. Single-stage  
Any zone; conventional heat-cool. Multistage  
T874D/Q674B Not applicable  
T874D/Q674D Not applicable  
Zone 1; conventional  
heat-cool.  
Zones other than zone 1; Not applicable  
conventional heat-cool  
Multistage  
and heat pump.  
Not applicable  
T874D/Q674E Not applicable  
Any zone; conventional heat-cool. Multistage  
a
Subbase not included with thermostat; order separately.  
TABLE 2—THERMOSTAT/SUBBASE SPECIFICATIONS.  
Thermostat/  
Anticipator Range (A)  
Thermostat/Subbase  
Switching  
System  
Subbase  
Color  
Heating  
(Adj.)  
Cooling  
(Fixed)  
Order Numbera  
Fan  
T874A1465/Q674B1471 HEAT-OFF-COOL  
T874A1465/Q674D1123 None  
ON-AUTO White/Gray  
None White/Gray  
Stg. 1—  
0.1 to 1.2  
Stg. 1—  
0 to 1.5  
T874A1465/Q674E1379 HEAT-OFF-COOL-AUTO ON-AUTO White/Gray  
T874D1801/Q674B1463 HEAT-OFF-COOL  
T874D1827/Q674B1471 HEAT-OFF-COOL  
T874D1801/Q674D1115 None  
ON-AUTO Beige/Brown  
ON-AUTO White/Gray  
Stg. 1—  
0.1 to 1.2;  
Stg. 2—  
Stg. 1—  
0 to 1.2;  
Stg. 2—  
0 to 1.0.  
None  
Beige/Brown  
White/Gray  
T874D1827/Q674D1123 None  
None  
0.1 to 1.0.  
T874D1827/Q674E1379 HEAT-OFF-COOL-AUTO ON-AUTO White/Gray  
a
Subbase not included with thermostat; order separately.  
Operation  
Recycling Notice  
On a 2-heat thermostat, the two stages of heat make  
This control contains mercury in a sealed tube. Do not  
place control in the trash at the end of its useful life.  
If this control is replacing a control that contains mercury  
in a sealed tube, do not place your old control in the trash.  
Contact your local waste management authority for  
instructions regarding recycling and the proper disposal of  
this control, or of an old control containing mercury in a  
sealed tube.  
sequentially as the temperature drops. Make refers to the  
mercury switch initiating a call for heat or cool.  
There are about 2° F [1° C] between stages so that the  
second stage makes only when the first stage cannot  
handle the load. This is the interstage differential.  
If you have questions, call Honeywell at 1-800-468-1502.  
S. M. • Rev. 6-93 •  
• ©Honeywell Inc. 1993 • Form Number 69-0580—2  
M3375  
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Installation  
Fig. 1—Installation of subbase on outlet box.  
WHEN INSTALLING THIS PRODUCT…  
. Read these instructions carefully. Failure to fol-  
1
low them could damage the product or cause a hazard-  
ous condition.  
2
. Check the ratings given in the instructions and on  
the product to make sure the product is suitable for your  
application.  
HORIZONTAL  
OUTLET  
BOX  
1
3
. Installer must be a trained, experienced service  
SUBBASE  
technician.  
1
NOT INCLUDED WITH UNIT.  
M3703  
4
. After installation is complete, check out product  
operation as provided in these instructions.  
Fig. 2—Installation of subbase on wall.  
CAUTION  
!
1
. Disconnect power supply to prevent electrical  
shock or equipment damage.  
WALL  
2
. To prevent interference with the thermostat  
linkage, keep wire length to a minimum and  
run wires as close as possible to the subbase.  
. Do not overtighten thermostat captive mount-  
ing screws, because damage to subbase threads  
can result.  
WIRES THROUGH  
WALL OPENING  
3
4
. Do not short across terminals of systems con-  
trols. This can burn out the thermostat heat  
anticipator.  
WALL  
ANCHORS  
2)  
MOUNTING  
HOLES  
(
MOUNTING  
SCREWS (2)  
M926  
SUBBASE  
IMPORTANT: Thermostats are calibrated at the factory by  
using subbases mounted at true level. Inaccurate sub-  
base leveling will cause thermostat control deviation.  
Fig. 3—Subbase components and leveling  
procedure.  
LOCATION  
Locate the subbase about 5 ft [1.5 m] above the floor in  
an area with good air circulation at average temperature.  
Do not mount the subbase where the thermostat may be  
affected by:  
TOP  
MOUNTING  
HOLES (2)  
WIRING  
TERMINAL  
THERMOSTAT  
CABLE OPENING  
SPIRIT LEVEL  
drafts or dead spots behind doors and in corners.  
hot or cold air from ducts.  
radiant heat from sun, appliances or fireplace.  
concealed pipes and chimneys.  
unheated (uncooled) areas such as an outside wall  
behind the thermostat.  
MOUNTING THE SUBBASE  
The thermostat subbase can be mounted on a horizontal  
outlet box or directly on the wall.  
MOUNTING  
HOLES (2)  
POST (2) FOR  
MOUNTING  
THERMOSTAT  
TO SPRING FINGER  
CONTACTS ON THE  
THERMOSTAT  
(UP TO 12)  
M927  
1. To mount on a horizontal outlet box, install the sub-  
base on the outlet box as shown in Fig. 1.  
For a wall installation, hold the subbase in position and  
mark holes for the anchors (Fig. 2). Obtain wall anchors  
locally. Take care that the wires do not fall back into the  
wall opening. Set aside subbase. Drill two 3/16 in. [4.8 mm]  
holesandgentlytapanchorsintotheholesuntilflushwiththe  
wall.  
4
. Level the subbase using a spirit level, as shown in  
Fig. 3, and firmly tighten the subbase mounting screws.  
The subbase mounting holes allow minor out-of-level  
adjustments.  
IMPORTANT: An incorrectly leveled subbase will cause  
2. Pull electrical wires through the cover plate (if used)  
the temperature control to deviate from set point.  
and subbase cable opening (Fig. 3). See Wiring the Sub-  
base section before pulling any wires.  
WIRING THE SUBBASE  
All wiring must comply with local electrical codes and  
ordinances. Follow equipment manufacturer wiring in-  
structions when available. To wire subbase:  
IMPORTANT: Use 18 gauge, color-coded thermostat  
cable for proper wiring.  
1
. Connect wires to the subbase terminals. Refer to  
3
. Secure the subbase with the screws provided. Do not  
Figs. 6-10 for wiring diagrams of typical zone systems. A  
fully tighten the subbase screws.  
2
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letter code is located near each subbase terminal for identi-  
fication. The terminal barrier permits straight or conven-  
tional wraparound wiring connection (Fig. 4).  
Fig. 5—Jumper RC and RH terminals for single  
transformer system. Strip wire 3/4 in. [19 mm].  
2
. Some Q674 Subbases have RC and RH terminals  
for isolated heating and cooling transformers. For zoning  
systems, jumper RC and RH terminals as shown in Fig. 5  
and wire as single R terminal.  
3
. Firmly tighten each terminal screw.  
4. Fit wires as close as possible to the subbase. Push  
RC  
RH  
excess wire back into hole.  
5. Plug the hole with nonflammable insulation to pre-  
vent drafts from affecting the thermostat.  
Fig. 4—Wiring connections.  
FOR STRAIGHT  
INSERTION–  
STRIP 5/16 in. [8 mm]  
FOR WRAPAROUND–  
STRIP 7/16 in. [11 mm]  
BARRIER  
SUBBASE TERMINAL SCREW  
RC  
RH  
M928  
M929  
Fig. 6—Typical hookup for MM-2 Mini-zone Control Panel with T874A Thermostat/Q674B,D Subbase in  
single-stage heating-cooling two-zone system.  
T874A THERMOSTAT/  
T874A THERMOSTAT/Q674B SUBBASE  
Q674D SUBBASE  
2
3
4
4
3
O
G
B
Y1 RC RH W1 W2 Y2  
Y1 Y2 RC RH W2 W1  
MINIZONE  
MM-2)  
(
CONTROL  
PANEL  
HEAT  
COOL  
ZONE 1 ZONE 2  
RELAY RELAY  
RELAY RELAY  
Y2  
Y1  
O
G2  
G1  
RC  
RH  
B
CHANGEOVER  
CONTROL  
TO SINGLE-  
STAGE  
HEATING/  
COOLING  
EQUIPMENT  
ZONE 1  
T6  
ZONE 2  
T6  
COOL O1  
FAN G1  
HEAT B1  
B
T5  
T4  
T5  
T4  
W2  
W1  
E
M6  
M4  
M1  
M6  
M4  
M1  
24 V, 40 VA  
TRANSFORMER  
2
1
L2  
4
5
6
Z
X
4
1
5
6
Z
X
1
L1  
HOT)  
DAMPER  
ACTUATOR  
DAMPER  
ACTUATOR  
(
1
2
3
2
3
1
2
3
4
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.  
ZONE 1 O AND B TERMINALS MUST BE CONNECTED FOR PROPER SYSTEM OPERATION.  
JUMPER RC AND RH TERMINALS TOGETHER AND WIRE AS SINGLE R TERMINAL.  
DO NOT CONNECT W2 AND Y2 TERMINALS TO CONTROL PANEL.  
M1633  
3
69-0580—2  
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MOUNTING THE THERMOSTAT  
. Remove the thermostat cover by pulling the bottom  
edge of the cover outward away from the base until it snaps  
free from the cover clip.  
spring fingers are not bent flat, preventing proper electri-  
cal contact with the subbase.  
4. Set the heat anticipator indicator(s) to 0.1A for  
proper system operation (Fig. 11).  
1
5
. Note the two tabs on the top inside edge of the  
NOTE: The cover is hinged at the top and is removed by  
pulling out at the bottom.  
thermostat base. The tabs fit into the corresponding slots  
on the top of the subbase. Mount the thermostat on the  
subbase. See Fig. 12.  
2
. Carefully remove and discard the polystyrene packing  
insert that protects the mercury switches during shipment.  
. Turn over the thermostat base and note the spring  
fingers that engage the subbase contacts. Make sure the  
6. Align the two captive mounting screws in the thermo-  
stat base with the posts on the subbase (Fig. 12). Tighten  
both screws. Do not overtighten the screws or damage to  
the subbase posts can result.  
3
Fig. 7—Typical hookup for MABS II and MABS II-L Control Panels with T874A Thermostat/Q674B,D  
Subbases in single-stage heating-cooling zone system. MABS II Control Panel shown; MABS II-L Control  
Panel hookup is the same.  
T874A THERMOSTAT/  
Q674D SUBBASE  
T874A THERMOSTAT/  
Q674D SUBBASE  
T874A THERMOSTAT/Q674B SUBBASE  
2
2
4
2
4
3
4
O
G
B
Y1 RC RH W1 W2 Y2  
Y1 Y2 RC RH W2 W1  
Y1 Y2 RC RH W2 W1  
MABS II  
CONTROL PANEL  
EM. HEAT SECOND FAN  
HEAT  
RELAY RELAY  
COOL  
RELAY  
CAC  
RELAY  
ZONE 1 ZONE 2  
RELAY RELAY  
ZONE 3  
RELAY  
RELAY  
STAGE  
RELAY  
Y
2
Y
1
O
ZONE 1  
ZONE 2  
ZONE 3  
G
2
G
1
T
8
T
7
T
8
T
7
T
8
T
7
CHANGEOVER  
CONTROL  
TO SINGLE-  
STAGE  
HEATING/  
COOLING  
EQUIPMENT  
R
C
R
H
COOL  
O
1
T
6
T
5
T
6
T
5
T
6
T
5
FAN  
HEAT  
G
1
ADD-A-  
ZONE  
A
4
A
3
B
B
1
E
1
T
4
M
6
T
4
M
6
T
4
M
6
W
2
EM. HEAT  
24 V, 40 VA  
W
1
E
A
2
A
1
2
M
4
M
1
M
4
M
1
M
4
M
1
1
TRANSFORMER  
1
L2  
4
1
5
6
Z
X
4
1
5
6
Z
X
4
1
5
6
Z
X
DAMPER  
ACTUATOR  
DAMPER  
ACTUATOR  
DAMPER  
ACTUATOR  
L1  
HOT)  
(
2
3
2
3
2
3
1
2
3
4
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.  
JUMPER RC, RH TOGETHER AND WIRE AS SINGLE R TERMINAL.  
ZONE 1 O AND B TERMINALS MUST BE CONNECTED FOR PROPER SYSTEM OPERATION.  
DO NOT CONNECT W2 AND Y2 TERMINALS TO CONTROL PANEL.  
M1634  
4
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Fig. 8—Typical hookup for MABS II and MABS II-L Control Panels with T874D Thermostat/Q674B,D  
Subbases in multistage heating-cooling zone system. MABS II Control Panel shown; MABS II-L Control  
Panel hookup is the same.  
T874D THERMOSTAT/  
Q674D SUBBASE  
T874D THERMOSTAT/  
Q674D SUBBASE  
T874D THERMOSTAT/Q674B SUBBASE  
2
3
4
2
4
2
4
RC  
O
G
B
Y2 W2 Y1 RH W1  
RC Y2 W2 Y1 RH W1  
RC Y2 W2 Y1 RH W1  
MABS II  
CONTROL PANEL  
EM. HEAT SECOND FAN  
HEAT  
RELAY RELAY  
COOL  
RELAY  
CAC  
RELAY  
ZONE 1 ZONE 2  
RELAY RELAY  
ZONE 3  
RELAY  
RELAY  
STAGE  
RELAY  
Y2  
Y1  
O
ZONE 1  
T8  
ZONE 2  
T8  
ZONE 3  
T8  
G2  
G1  
RC  
RH  
B
CHANGEOVER  
CONTROL  
TO SINGLE-  
STAGE  
HEATING/  
COOLING  
EQUIPMENT  
T7  
T6  
T5  
T4  
M6  
M4  
M1  
T7  
T6  
T5  
T4  
M6  
M4  
M1  
T7  
COOL O1  
FAN G1  
T6  
ADD-A-ZONE  
A4  
T5  
HEAT  
EM. HEAT  
24 V, 40 VA  
B1  
E1  
2
T4  
W2  
W1  
E
A3  
A2  
M6  
M4  
M1  
A1 TRANSFORMER  
1
1
L2  
4
1
5
6
Z
X
4
1
5
6
Z
X
4
1
5
6
Z
X
DAMPER  
ACTUATOR  
DAMPER  
ACTUATOR  
DAMPER  
ACTUATOR  
L1  
(HOT)  
2
3
2
3
2
3
1
2
3
4
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.  
JUMPER RC, RH TOGETHER AND WIRE AS SINGLE R TERMINAL.  
ZONE 1 O AND B TERMINALS MUST BE CONNECTED FOR PROPER SYSTEM OPERATION.  
IF SINGLE-STAGE COOLING, DO NOT CONNECT Y2; IF SINGLE-STAGE HEATING, DO NOT CONNECT W2.  
M1393A  
5
69-0580—2  
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Fig. 9—Typical hookup for MABS XX Control Panel with T874A Thermostat/Q674B,E Subbases in single-  
stage heating-cooling zone system.  
MABS XX  
CONTROL PANEL  
ZONE 1  
FAN  
ZONE 2  
FAN  
ZONE 3  
FAN  
HEAT  
COOL  
HEAT  
COOL  
HEAT  
COOL  
1
MCM  
2
3
CAC  
FC  
ZONE 1  
FAN  
ZONE 2  
FAN  
ZONE 3  
FAN  
4
5
ZONE SYS  
ZONE SYS  
ZONE SYS  
6
7
DAMPER  
DAMPER  
DAMPER  
TO SINGLE-  
STAGE  
HEATING/  
COOLING  
EQUIPMENT  
8
9
Y
W
G
Gh  
O
B
RC RH  
OPEN CLOSE OPEN CLOSE OPEN CLOSE  
ZONE 1  
ZONE 2  
M6 M4 M1 VO VC  
ZONE 3  
W
M6 M4 M1 VO VC  
1
2
G
G
Y
R
W
M6 M4 M1 VO VC  
G
Y
R
W
G
G
Y
R
G
Y1  
Y2  
1
Y1  
Y2  
Y1  
Y2  
L2  
L1  
(HOT)  
R
R
R
W1  
W1  
W1  
2
2
2
W2  
O
W2  
O
W2  
O
4
5
6
Z
X
4
1
5
6
Z
X
4
1
5
6
Z
X
B
DAMPER  
ACTUATOR  
B
DAMPER  
ACTUATOR  
B
DAMPER  
ACTUATOR  
T874A  
T874A  
T874A  
1
2
3
2
3
2
3
THERMOSTAT/  
Q674B OR E  
SUBBASE  
THERMOSTAT/  
Q674B OR E  
SUBBASE  
THERMOSTAT  
Q674B OR E  
SUBBASE  
1
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.  
2
WIRE ONLY THE TERMINAL CONNECTIONS SHOWN. SOME TERMINALS NOT AVAILABLE ON ALL THERMOSTATS. IF THERMOSTAT HAS  
R/RC/RH TERMINALS, JUMPER TOGETHER AND WIRE AS SINGLE R TERMINAL. DO NOT CONNECT THERMOSTAT O AND B TERMINALS  
TO CONTROL PANEL.  
M1636  
6
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Checkout  
Before beginning checkout of thermostat operation,  
set switches on the control panel for the desired system  
operation. See instructions provided with the control panel.  
To set up the system for thermostat checkout, adjust  
each thermostat settings as shown in Table 5.  
TABLE 5—SYSTEM SET-UP FOR THERMOSTAT CHECKOUT.  
Heating  
Cooling  
Zones Other  
Control  
Panel  
Zones Other  
Than Zone 1  
Zone 1  
Zone 1  
Than Zone 1  
Mini-zone  
MABS II  
MABS II-L  
Set thermostat  
Move the heating set  
point lever 10° F  
[6° C] below room  
temperature.  
Set thermostat  
system switch to  
COOL; set fan  
switch to AUTO.  
Move the cooling  
set point lever 10° F  
[6° C] above room  
temperature.  
Move the cooling set  
point lever 10° F  
[6° C] above room  
temperature.  
system switch to  
HEAT; set fan switch  
to AUTO. Move the  
heating set point  
lever 10° F [6° C]  
below room  
temperature.  
MABS XX  
On all zone thermostats, set the system  
switch to HEAT; set the fan switch to AUTO.  
Move the heating set point lever 10° F [6° C]  
below room temperature.  
On all zone thermostats, set the system  
switch to COOL; set the fan switch to AUTO.  
Move the cooling set point lever 10° F [6° C]  
above room temperature.  
NOTE: The control panel provides a three-  
minute time delay when 24V is applied to  
the control panel and at the end of each  
equipment cycle. The high-speed fan runs  
during this time delay.  
NOTE: The control panel provides a three-  
minute time delay when 24V is applied to  
the control panel and at the end of each  
equipment cycle. The high-speed fan runs  
during this time delay.  
HEATING  
COOLING  
NOTE: If a plenum fan control is used in the heating  
system, there will be a short delay on a call for heat to  
allow the furnace to heat the plenum. The fan starts  
immediately in electric heat systems. Allow 30 seconds  
for the damper to open or close completely.  
CAUTION  
!
Do not operate cooling equipment if outdoor  
temperature is below 50° F [10° C]. Refer to  
manufacturer recommendations.  
Make sure all zone thermostats are set as instructed in  
the Heating column in Table 5. Check each zone thermo-  
stat as follows:  
Make sure all zone thermostats are set as instructed in  
the Cooling column in Table 5. Check each zone thermo-  
stat as follows:  
1
. If thermostat has a fan switch, set it to ON. See  
1
. Move cooling set point lever on the zone thermostat  
0° F [6° C] below room temperature to call for cooling.  
. After 30 seconds, place your hand in front of an air  
register in that zone to check for cool air at the register.  
. Move the cooling set point lever on the zone thermo-  
Fig. 13. After 30 seconds, place your hand in front of an  
air register in that zone to check for air flow at the register.  
1
2
2
. Reset fan switch, if provided, to AUTO. After 30 sec-  
onds, make sure air flow at register has stopped.  
. Move heating set point lever on zone thermostat  
0° F [6° C] above room temperature to call for heat.  
. After 30 seconds (longer, if necessary, for time delay  
on plenum fan control), check for warm air at the register.  
. Move heating set point lever on the zone thermostat  
0° F [6° C] below room temperature to end a call for heat.  
3
3
stat 10° F [6° C] above room temperature to end the call for  
cooling. After 30 seconds (longer, if necessary, for time  
delay on control panel), check that air flow at the register  
has stopped.  
1
4
5
4. Repeat steps 1-3 for each zone thermostat.  
1
After 30 seconds (longer, if necessary, for time delay on  
plenum fan control or control panel), check that air flow at  
the register has stopped.  
When system checkout is complete, return all thermo-  
stats to the desired settings for normal system operation.  
6. Repeat steps 1-5 for each zone thermostat.  
9
69-0580—2  
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Calibration  
Fig. 14—Thermometer calibration.  
THERMOSTAT  
T874 thermostats are accurately calibrated at the  
factory. They do not have provision for field calibration.  
THERMOMETER  
The thermometer in your thermostat has been accu-  
rately calibrated at the factory. The thermometer should  
only need adjustment if it has been dropped or shifted due  
to mishandling.  
If the set point lever and the thermometer reading do  
not agree:  
1
. Remove the thermostat cover by pulling up from the  
bottom of cover until it clears the mounting slots.  
. Set the thermostat cover on a table near an accurate  
thermometer.  
2
3. Allow ten minutes for the cover thermometer to  
sense the area temperature; compare the readings. Be care-  
ful not to touch the thermometer or breathe on it.  
M5070  
4
. If the readings are the same, replace the cover and put  
the system into operation.  
. If the readings are different, insert a small screw-  
5
driver in the thermometer slot (Fig. 14) and turn it until the  
thermometers have the same reading.  
6. Replace the thermostat cover and put the system into  
operation.  
NOTE: Hand heat will offset the thermometer reading.  
After making each adjustment, wait ten minutes for  
the thermometer to stabilize before comparing.  
Home and Building Control  
Honeywell Inc.  
Home and Building Control  
Honeywell Limited—Honeywell Limitée  
740 Ellesmere Road  
Helping You Control Your World  
1985 Douglas Drive North  
Golden Valley, Minnesota 55422  
Scarborough, Ontario  
M1P 2V9  
QUALITY IS KEY  
Printed in U.S.A.  

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